This invention relates to an apparatus and method for chromatographic separation of organic compounds, and particularly to improvements in flash chromatography.
In contrast to more conventional high-resolution absorption chromatography techniques, which may generally be used to effect purification of samples as large as 1-2 grams and require 1-3 hours, flash chromatography permits separation of samples of up to several grams in a relatively short time with moderate resolution. This now popular technique was first described by Still, et al., J. Org. Chem. 43, 2923 (1978).
In conventional flash chromatography, a column is filled with sorbent. After loading the chemical to be purified into the top of the sorbent, a reservoir on the top of the column is filled with solvent. This solvent is then delivered through the column, eluting the sample downward at a rate based on its affinity to the solvent and the sorbent.
Although flash chromatography has enjoyed widespread acceptance as a rapid, moderate resolution purification technique, it suffers from disadvantages in convenience, safety and reliability. For example, the amount of solvent that can be used without interruption of elution is dependent on the size of the reservoir attached to the top of the column. Beyond a certain point, increases in reservoir size can lead to a top-heavy apparatus. Moreover, if the reservoir is too small, interruption of elution to introduce additional solvent can affect the accuracy of the separation. Maintaining an inventory of various-sized reservoirs adds to equipment cost. As the length of the column increases, the danger and inconvenience of loading solvent into a reservoir at the top of the column is multiplied. Finally, access to the top of the column necessitates removal of the large solvent reservoir with attendant danger and inconvenience.
Another significant problem with conventional flash chromatography systems is the pressure control valve. In those systems, the top of the solvent reservoir on top of the column is connected directly to the pressurized air source. Pressure is regulated with a bleed valve. Air is constantly flowing into the reservoir and out of the bleed valve. One problem with this arrangement is that the head of air over the solvent is dynamic; i.e., the air is constantly exchanged. Contamination of the solvent with water, compressor oil, fitting grease, and other residual entrained substances is possible. An even more significant problem is glassware explosions. Flash chromatography reservoirs are notoriously susceptible to exploding from overpressurization, fluctuations in pressure, or fatigue. And when the reservoir is roughly in the vicinity of the chemist's head, as it is in a conventional system, the dangers of such an explosion are multiplied.
The use of multiple solvents for packing the column and/or eluting the sample is impossible in a conventional system without interrupting elution.
Accordingly, one object of the present invention is to provide an apparatus that can deliver any desired volume of solvent to a flash chromatography column.
Another object of the present invention is to provide a flash chromatography apparatus that eliminates the solvent reservoir at the top of the column.
Still another object of the present invention is to provide a flash chromatography apparatus characterized by more convenient and ready access to the top of the column.
A further object of the present invention is to provide a method for performing flash chromatography that eliminates interruptions in elution for addition of solvent.
Still another object of the present invention is to reduce the danger of solvent reservoir explosions.
Yet another object of the present invention is to provide a two-solvent capability for flash chromatography systems.
Another object of the present invention is to provide a flash chromatography apparatus wherein solvent contamination is minimized by using a relatively static head of gas to pressurize the solvent reservoir.